This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We previously reported a comparative study of the in vivo infectivity and pathogenicity of a CCR5-tropic SHIVSF162 P4 in rhesus and pig-tailed macaques. Results indicate that both rhesus and pig-tailed macaques are similarly susceptible to SHIVSF162 P4 infection by mucosal routes. However, SHIV replication was significantly more robust in pig-tailed macaques than in rhesus. Since, persistent viral infection has been correlated with broadening of neutralizing antibody responses, we continued to monitor the evolution of viral sequences and neutralizing antibody activities in a subset of infected pig-tailed macaques after the primary goal of this study was achieved. Information obtained from these studies may help the establishment of macaque models to determine factors required for the generation of broadly neutralizing antibodies against HIV-1.